Regulation of dynamo-electric machines.



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REGULATION OF DYNAIO ELECTRIC IACI'IINES.

(Application flhd Inn. v1'], 1900.)

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m. 7l2,56|. Patented Nov. 4, I902.

' A. u. LUNT.

REGULATION OF DYNAIC ELECTRIC MACHINES.

A umion filed 1m. 17, 1900.

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Witnesses. Inventor (922d AlexanderDLuno.

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UNITED STATES PATENT OFFICE.

ALEXANDER D. LUNT, OF SOHENEOTADY, NEW YORK, ASSIGNOR TO THE GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

REGULATION OF DYNAMO-ELECTRIC MACHINES.

SPECIFICATION forming part of Letters Patent No. 712,561, dated November4, 1902.

Application filed January 1'7, 1900. Serial No. 1,727. (No model.)

To all whom it may concern:

Be it known that I, ALEXANDER D. LUNT, a citizen of the United States,residing at Schenectady, county of Schenectady, State of 5 New York,have invented certain new and useful Improvements in Regulation ofDynamo-Electric Machines, (Case No. 1,371,) of which the following is aspecification.

Then an ordinary rotary converter is into verted in function, whereby itreceives energy in the form of direct current and delivers alternatingcurrent, its speed is dependent upon its field strength except in thecase where the converter is coupled in multiple :5 with a constantspeedalternator or other source of alternating current of steady frequency.If without being connected to a source of alternating current of steadyfrequency the converter is used to supply alterzonating-current-translating devices, its speed is subject to widevariations, due to the effect of the reaction of wattless current in thearmature upon the field strength of the machine. If, for example, theconverter supplies a load which takes a considerable lagging current,then the demagnetizing effect of this current upon the field of theconverter may be such as to cause a dangerous increase in speed. Toovercome this difficulty and prevent any mishaps which might arise fromdangerously high speed in the converter, many devices have beenproposed. So far as I am aware, however, all of these devices requirethe speed of the converter to increase above the normal before they arebrought into operation and their useful effects obtained.

My present invention aims to compensate for the armature reaction ofthealternating current supplied by the converter, and in its operationanticipates the variation in speed which otherwise would result from achange in field strength.

The nature of my invention and its mode of operation will be betterunderstood by reference to the following description, taken inconnection with the accompanying drawings, while its scope will beparticularly pointed out in the claims appended hereto.

Figure 1 illustrates an apparatus embody- 5o ing my invention[ Fig. 2 isa partial diagram of circuits of the apparatus shown in Fig. l, and Fig.3 is a modification.

As briefly mentioned above, the variations in speed of such invertedrotary converters are principally due to the varying reaction ofwattless armature-currents upon the field strength. The most efiectiveregulation in speed is therefore that which employs means responsivedirectly to variations in the wattless component of the alternating loadand not one which depends for its eifectiveness upon variations in speedof the machine. The one is directly responsive to the cause of speedvariation, while the other acts only after the speed commences to vary.

My invention consists, therefore, in the utilization of field-regulatingmeans responsive directly to variations in the amount of leading orlagging current in the alternatingcurrent circuit of the machine.Various means may be employed for securing this result, some of which Iherein describe as illustrating my invention. That other apparatus maybe employed for securing the beneficial effects of my invention will beobvious to those skilled in the art.

To secure the best effects, I prefer to employ a regulatingdynamo-electric machine driven synchronously with the inverted rotaryconverter and operating to supply an electromotive force directlyproportional to the amount of wattless alternating current in the mains.The field of the converter may, if desired, be excited entirely fromthis source of electromotive force or by the resultant effect of thiselectromotive force and of current derived from some source of constantpotentialsuch, for example, as the directcurrent-supply mains, to whichthe inverted rotary is connected.

Fig. 1 shows an apparatus of this description. The armature of aninverted rotary converter is indicated at 1 and its field-magnet at 2.Direct current is supplied to the commutator of the machine fromdirect-current mains 3 4. Upon the same shaft with the armature 1 ismounted the armature 5 of a regulating-machine of the direct-currenttype. The armature of this machine is provided with two distinctwindings and in struc- I00 ture resembles somewhat an ordinarymotorgenerator. One of the windings is connected to a commutator 6 andoperates in the same manner as the generating-winding of adirect-current machine. Brushes bear upon the commutator 6 and areconnected to the shunt field-winding '7 and to an external circuit 8.The circuit 8 is arranged so as to include the armature 5 of theregulating-machine in series with the field-winding 9 of the converter,which field winding is supplied with current from thedirect-current-supply mains 3 4.. It will thus be seen that the electromotive force of the regulating-machine is combined with thatimpressed upon the converter field-winding from the direct-currentmains.

In order to secure the necessary variation in the electromotive force ofthe regulatingmachine in response to variation of power factor of thealternating-current load supplied by the inverted rotary converter, theregulating-machine is provided with a second winding arranged in series'with the alternating leads brought out from the armature of theconverter. These leads are shown in the drawings at 9. They pass fromthe winding of the converter-armature 1 through the second winding onthe regulating-machine and then to collector-rings 10, from whichcurrent is led off to suitable translating devices-such, for example, aslamps L, motors M, and the like. The arrangement of these circuits willbest be understood by a brief reference to Fig. 2. Here the armature ofthe inverted rotary is indicated at 1. The alternating-current leads 9are shown as proceeding therefrom and passing through the series winding11 on the armature of the direct-current-regulating machine and then tothe collector-rings 10, from which current is distributed to translatingdevices. The armature of the regulating-machine isprovided with a secondwinding 12, this winding being connected to a commutator in the usualway and by its rotation serving to generate a continuous electrornotiveforce.

When in operation, the winding 12 generates an electromotive force ofapproximately constant value so long as the amount of wattlesscurrentfiowingin the winding 11 remains constant. When, however, thewattless current varies, its reaction upon the field of theregulating-machine alters the field strength, and consequently altersthe electromotive force derived from the winding 12, thereby producing acorresponding change in the field magnetization of the invertedconverter. In explanation of this action it may be stated that thecurrent flowing in the winding 11 produces a rotary field revolving witha frequency corresponding to the speed of the inverted rotary. Theconnections to the winding 11 are made in such a way as to cause thedirection of rotation of the field to be opposite to the direction ofrotation of the shaft. The shaft rotates in one direction as fast as thefield rotates with respect to the shaft, and the field therefore becomesfixed in space. The field-magnet 13 is arranged so that the flux set upby this field causes merely across magnetization inthe field-poles whenthe inverted converter is operating at unit power factor. If under theseconditions the alternating current commences to lag, then the flux inthe regulating-machine due thereto would rotate slightly in space and bebrought partially into line with the field magnetization, therebyreducing the efiective magnetic flux of the machine and so reducing itselectromotive force. This reduction in the electromotive force of theregulating-machine causes an increase in the current flowing in thefield-winding of the converter, since in this instance theregulating-machine is connected in opposition to the electromotive forceimpressed on the converter fieldwinding. The increase in speed of theconverter which would ordinarily be caused by the weakening of its fielddue to the reaction of lagging currents in the armature is in this casecompensated for by the increase in field ampereturns which takes placedirectly in response to variation in wattless current supplied by theconverter. The field magnetomotive force is thus increased as soon asany opposition thereto is presented by the reaction of laggingarmature-currents.

It will be understood that with leading currents the opposite efiec'ttakes place, the field magnetomotive force of the converter beingdecreased to compensate for the magnetizing efiect of leading currentsin the armature.

Although I have shown the regulating-machine as provided with a fieldstructure 13 having an exciting-winding, I may, if desired, omit theexciting-winding and produce the requisite magnetization of the fieldentirely by the reaction of wattless currents in the armature. In thiscase the field magnetization will be zero at unit power factor and willincrease from zero by an amount dependent upon the value of wattlesscurrent flowing. Since the field thus operates below saturation, itsvariation in strength will be almost exactly proportional to theVariation in wattless current, and the electromotive force developed atthe commutator of the machine will therefore correspond. If thealternatingcurrent load is liable to change from lagging to leading orthe reverse,I prefer to provide the field with amagnetizing-winding, asshown, and to vary the field strength above and below a certain selectedpoint below the point of saturation. If no field-winding were employed,the effect of hysteresis upon changing from lagging to. leading currentor the reverse would cause the field magnetization for a given value oflagging current to be difierent from that corresponding to the samevalue of leading current, which is an undesirable result.

While I have shown the regulating-machine as employed merely for thepurpose of varying the amount of current flowing in the field of theconverter, it will be evident, as before stated, that this machine maybe employed for supplying the total excitation, in which case theconnection of the converter-field with the direct-current mains 3 4would be omitted.

Fig. 3 shows a somewhat different arrangement of apparatus, thedifference being that the regulating-machine in this case is providedwith but a single winding, to which both commutator and collector ringsare connected. The collector-rings are supplied with electromotiveforces derived from the secondaries of series transformers T T T whoseprimaries are connected in series with the alternating-current mains 14,15, and 16. The connection of the collectorrings with the winding of thearmature 17 is made so that the direction of the rotation of the fielddue to the alternating currents is opposite to the direction of rotationof the armature, whereby, as before, this field is caused to bestationary in space. As the wattless current in the alternating-currentmains changes the field strength of the regulating-machine iscorrespondingly changed in the manner above briefly described. In otherrespects the action of the arrangement shown in Fig. 3 is the same asthat shown in Fig. 1, so that it is therefore unnecessary to refer againin detail to parts of the apparatus shown in Fig. 3, but notspecifically mentioned.

In Figs. 1 and 3 the field-windings are arranged to produce certainpolarities in the pole-pieces. This relation of polarities may becorrect for a given number of poles and incorrect for another, and it istherefore to be understood that in carrying out the invention inpractice the fields are to be wound in a direction suitable forproducing the requisite relationofpolaritiesinthefield-poles. Thus, forexample, if Fig. 3 were supposed to represent a machine having two polesthen the field-winding would be incorrectly shown, since the two poleswould be of the same polarity. If, however, it be supposed that thearrangement represents a six-pole machine, the direction of the windingswould be correct. What I claim as new, and desire to secure by LettersPatent of the United States, is

1. The method of maintaining inverted rotary converters at constantspeed, which consists in automatically varying the field ampere-turns inresponse to variation in lag or lead of the alternating current suppliedby the converter and irrespective of variations in speed thereof.

2. The method of maintaining inverted rotary converters at constantspeed, which consists in impressing on the field-winding of theconverter two electromotive forces one of which is constant and theother variable.

3. The method of maintaining inverted rotary converters at constantspeed, which consists in impressing on the field-windings of theconverter two electromotive forces one of which is constant, and theother variable in response to variation of power factor of thealternating-current load.

4. The, method of maintaining constant speed in an inverted rotaryconverter for transforming direct current to alternating current, whichconsists in exciting the field by the resultant effect of twoelectromotive forces, one of which is substantially constant and theother dependent upon the power factor of the alternating-current load.

5. The method of governing the speed of an inverted rotary converteremployed for transforming direct current to alternating current, whichconsists in exciting the field of the converter by the resultant effectof two electromotive forces, one of which is definitely related to theimpressed electromotive force on the direct-current mains, the other tothe wattless component of current flowing in th alternating-currentmains.

6. The method of operating a rotary converter, which consists insupplying energy thereto in the form of direct current, derivingalternating current therefrom of a frequency dependent on the fieldstrength of the converter, and compensating for the effect of wattlesscurrents in the armature upon the field strength, before the speed ofthe machine can be affected thereby.

In witness whereof I have hereunto set my hand this 13th day of January,1900.

ALEXANDER D. LUNT.

Witnesses:

BENJAMIN B. HULL, MABEL E. JAcoBsoN.

